Dressing ring for tubular expanded polystyrene cooling mandrel

ABSTRACT

A surface treating device to be attached to the upstream end of a cooling and sizing mandrel used in the manufacture of a web of expanded polystyrene of a general purpose grade from a warm, tubular extrudate of such material, such treating device serving to prepare the dense, radially innermost surface of such tubular extrudate so that it can be drawn over the cooled, cooling and sizing mandrel in tight, surface to surface contact therewith to substantially reduce the amount of material from the web which accumulates on the cooling and sizing mandrel.

United States Patent [191 Blackwelder [11] 3,871,802 ]Mar.l8,l975

[ DRESSING RING FOR TUBULAR EXPANDED POLYSTYRENE COOLING 264/47, 48;425/4 C, 8]? C, 72, 378, 379, 404, 325, 326 R, 387, 392, 393

3,765,808 lO/l973 Lyon et al 425/72 Primary Examiner-R. Spencer AnnearAssistant Examiner-Mark Rosenbaum Attorney, Agent, or Firm Thomas A.Meehan; Edward J. Holler [57] ABSTRACT A surface treating device to beattached to the upstream end of a cooling and sizing mandrel used in themanufacture of a web of expanded polystyrene of a general purpose gradefrom a warm. tubular extrudate of such material, such treating deviceserving to prepare the dense, radially innermost surface of such tubularextrudate so that it can be drawn over the cooled, cooling and sizingmandrel in tight, surface to surface contact therewith to substantiallyreduce the amount of material from the web which accumulates [56]References Cited on the cooling and sizing mandrel.

UNITED STATES PATENTS 3,426,111 2/l969 425/308 x 3 Clam", 2 DrawingFlgures 19 1 I? 13 .2; ill ii i f PATENTED HAR] 8 I975 FIG.

FIG. 2

BACKGROUND OF THE INVENTION It is well known in the art that sheets orwebs of expanded polystyrene, with opposed surfaces or skins ofsubstantially greater density than the intermediate core have manydesirable properties for many end product applications. For example,U.S. Pat. No. 3,468,467 to S. W. Amberg, which is now assigned toassignee of this application, shows a nestable, twopiece disposabledrinking cup for hot beverages in which the sidewall element isfabricated from a blank which is cut from a web of expanded polystyrenehaving dense surface skins, and copending application Ser. No. [59,443of S. W. Amberg et al., which is assigned to the assignee of thisapplication, now U.S. Pat. No. 3,760,968, shows a composite containercomprised of an inner glass envelope and, attached to and surroundingthe exterior thereof, a protective and externally decorated sleevefabricated from a web of oriented polystyrene.

As is shown, for example, in U.S. Pat. No. 3,560,600 to V. L. Gliniecki,webs of expanded polystyrene having dense surface skins may be producedfrom warm, blowing agent-containing, tubular extrudates of such materialby quickly chilling the inner and outer surfaces of the extrudate as itemerges from the die to inhibit further expansion of the residualblowing agent within the extrudate in the surface portions thereof, byallowing the residual blowing agent in the inner or core portion of theextrudate to continue to expand for some finite period of time, bydrawing the extrudate over an internally cooled mandrel of greaterdiameter than the extrusion die to size the diameter of the tube and tocool substantially all remaining residual blowing agent, and by slittingthe tube as it passes from the die along one or more longitudinallyextending lines to form one or more webs therefrom. Such an arrangementwill work reasonably well when the extrudate is comprised of asubstantial portion of a rubber-modified, impact grade of polystyreneand/or when the end products to be formed from the webs of suchpolystyrene do not require that the mandrel or radially innermostsurface of the extrudate be of high quality, for example, the qualityrequired to permit attractive printing or decorating material to beplaced thereon.

The tubular extrusion arrangement heretofore described can, however,lead to surface quality defects on the web surface which comprised theradially innermost or mandrel-contacting side of the extrudate from suchweb was formed. These defects can arise by the plating out" oraccumulation of material from the extrudate onto the mandrel by virtueof the tight, surface to surface contact between the extrudate and themandrel which is required for proper cooling of the extrudate. Suchaccumulation of material, which has been found to be especially severein the case of extrudates comprised of a substantial portion of generalpurpose grades of polystyrene because of the inherently brittlecharacter of such grades, causes scratching or marring of the surface ofthe extrudate which passes thereover, and this is particularlyobjectionable when it is desired to subsequently apply printing ordecorative material to such surface. To be able to operate at allaccording to such as arrangement with general purpose grades ofpolystyrene, it is necessary to very frequently shut the extrusion linedown to permit the mandrel to be cleaned or sand blasted, and thecostliness of such shut downs substantially detracts from the economicadvantages otherwise to be gained from the substitution of lessexpensive general purpose grades of polystyrene in applications whereimpact grades previously were used.

GENERAL DESCRIPTION OF THE lNVENTlON ln accordance with the presentinvention, however, there is provided a surface treating device which isattached to the upstream end of the cooling and sizing mandrel and whichtreats the radially innermost surface of the extrudate before itcontacts the mandrel to substantially reduce the tendency for materialfrom the extrudate to plate out on, or to transfer to, the mandrel, evenwhen the extrudate is comprised of a substantial portion of a generalpurpose grade of polystyrene. Such a device comprises a metallic ringwith a smooth, extrudate-contacting outer surface of approximately thesame outside diameter as the outside diameter of the mandrel, which ismounted substantially concentrically with the mandrel and which isaxially spaced in front of the mandrel by a short distance. The axiallength of such ring is short, in relationship to the axial length of themandrel. When such a ring is used, there is a substantial reduction inthe tendency of material in the extrudate to adhere to the mandrel, suchimprove ment being sufficient to permit the satisfactory production,over prolonged periods of time, of webs of expanded polystyrene ofmedium impact and general purpose grades with a printable, densemandrel-contacting skin. It is thought that such improvement is derivedfrom the mechanical ironing" or dressing" effect that the ring has onthe normal irregularities in the extrudate surface which would otherwiselead to the adhesion of particles of material from such surface on tothe mandrel surface, it being noted that the bearing pressure of suchring on the extrudate surface is probably somewhat greater than thebearing surface of the extrudate on the mandrel itself because of therelatively short axial length of the ring. It is also to be noted thatthe ring, being disposed away from the source of cooling from themandrel, will probably run with a some what higher extrudate-contactingsurface temperature than the mandrel, which may augment the mechanicalironing effect of the ring previously mentioned.

Accordingly, it is an object of the present invention to provideimproved method and apparatus for the cooling of a tubular extrudate ofexpanded polystyrene, especially one .comprised mainly of a generalpurpose grade of polystyrene, by the sliding contact of the dense innersurface or skin of such extrudate over a metallic cooling and sizingmandrel.

It is a further object of the present invention to provide method andapparatus for the production of a web of expanded polystyrene,especially one comprised mainly of a general purpose grade ofpolystyrene, such web having at least one surface or skin which is ofsubstantially greater density than the interior or core region of suchweb and which is of a satisfactory quality to receive printing ordecorative material to permit such surface to serve as the visible,outermost, decorated surface of drinking cups, glass containerprotective sleeves and the like.

It is a further object of the present invention to provide a web ofexpanded polystyrene, comprised mainly of a general purpose grade ofpolystyrene and having a relatively dense printable skin, which skin wasthe mandrel-contacting surface of a tubular extrudate from which suchweb was severed.

For a further understanding of the present invention and the objectsthereof, attention is directed to the drawing, to the followingdescription thereof to the detailed description of the invention and tothe appended claims.

DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary, elevational,cross-sectional view of apparatus which embodies the present inventionand which is useful in the production of webs of expanded polystyrene;and

FIG. 2 is a fragmentary, elevational, cross-sectional view, at anenlarged scale, of a portion of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE lNVENTlON As is well understood in the art,expanded polystyrene may be produced in the form of webs of sheets froma circular extrudate, and to this end, there is provided extrusion meanscomprising an annular extrusion die 11, shown fragmentarily, forextruding or expressing on a relatively continuous basis, a warmextrudate E of circular cross-section. The thickness of extrudate E isshown at an enlarged scale in the drawing for purposes of illustration.This extrudate contains residual blowing agent which expands when thepressure on the extrudate is released upon the exit of the extrudatefrom the die. Extrusion die ll may advantageously be constructed inaccordance with the teachings of copending application Ser. No. 2,005 inwhich I am a coinventor with Victor E. Scotto and which is assigned tothe assignee of this application, now US. Pat. No. 3,75 l ,537. However,it is believed that the present invention can also be advantageouslyutilized in conjunction with other known types of extrusion dies.

As the warm extrudate E issues from extrusion die 11, at least theradially innermost surface thereof is quickly chilled, to prevent thereduction in density of the extrudate near this surface due to expansionof the blowing agent, by directing streams of cooling air or other fluidthereagainst from a circular array of ports 12 in a longitudinal fluidinlet and mounting pipe 13 which is disposed coaxially with extrusiondie 11. Means, not shown, may also be provided to chill the radiallyoutermost surface of extrudate E as it emerges from die II to form anouter skin" thereon. The present invention may, however, beadvantageously practiced with or without such means. In any event, theextrudate E with the chilled innermost surface is then passed over asizing and cooling mandrel 14 which is mounted on pipe 13 somewhatdownstream of extrusion die 11, which is of a larger diameter than thediameter of the extrusion orifice of die 11 to positively fix the finaldiameter of extrudate E and which is internally cooled (in conventionalfashion by means not shown) to conductively cool the extrudate which isin surface to surface contact therewith and to thereby suppress itsfurther foaming or expansion by expansion of residual blowing agenttherein. As the extrudate traverses the finite distance from theextrusion die to the mandrel 14, the expansion of the blowing agentwithin the warm portions of the extrudate away from the chilled surfacethereof will cause the thickness of these portions to increase, with aresulting decrease in the density thereof. It is to be noted that someprior art tubular expanded polystyrene extrusion arrangements, such asthat shown in the aforesaid US. Pat. No. 3,560,600, maintain a thin filmof air between the extrudate and the cooling mandrel, which preventssurface to surface contact therebetween. The present invention isinapplicable to such an arrangement, but is quite beneficial when theuse of such an air film is intolerable, which is the case, for example,when the innermost surface of the extrudate must be of printablequality.

Mandrel 14 is of generally annular construction, the upstream anddownstream portions being closed by ported plate-like members 15 and 16,member 15 pref erably being cast integrally with the body of mandrel andmember 16 preferably being a separate piece mounted on a thickenedcentral hub 17. The ports in members 15 and 16 serve to vent toatmosphere the air or cooling fluid discharged through ports 12 againstthe extrudate, and the ports in members 15 and 16 are desirably sized tomaintain some positive pressure against the inner surface of theextrudate to facilitate its expansion from the diameter of the extrusiondie to the diameter of the mandrel.

To facilitate the surface to surface sliding movement of the extrudateover the mandrel, without the plating off" of material from theextrudate onto the mandrel, as heretofore explained, there is providedan extrudate surface contacting ring 18 mounted substantiallyconcentrically with mandrel l4 and having an outside diametersubstantially equal to the outside diameter of the mandrel. Contactingring has a rounded leading edge 18a and is axially separated from theupstream end of mandrel 14 by a spacer ring 19, whose outside diameteris less than that of contacting ring 18. Contacting ring may bemaintained in the position shown by bolting it to the mandrel by meansof a multiplicity of bolts 21, as shown in FIG. 2, each of which extendsthrough spacer ring 19 into the mandrel.

After the cooled extrudate E emerges from the downstream end of mandrel14 it is slit into one or more longitudinally extendings webs along anequal number of longitudinally extending lines by means of one orslitter blades 22, and each such web may be drawn through subsequentprocessing steps by conventional downstream winding rollers (not shown)which also serve to draw the extrudate over the cooling mandrel. In someinstances, it may be desirable to treat the radially outermost surfaceof each such web in advance of such winding rollers in the mannersuggested in my copending application Ser. No. 316,719, which is alsoassigned to the assignee of this application, for the purposes suggestedin such copending application.

The invention has been found to be especially advantageous whenproducing foam webs comprised mainly of general purpose grades ofpolystyrene such as that sold by Koppers under the designation 8G andthat sold by Dow Chemical under the designation XP-604 l. The inventionhas been successfully practiced with such resins over a range of webthicknesses from 10-40 mils (0010-0040 inch) and over a range of averageweb densities from 10-20 pounds per cubic foot. In the production offoam webs comprised mainly of a medium impact grade of polystyrene, suchas that sold by Dow Chemical under the designation 441, the inventionhas proved to be advantageous, in making less critical to properoperation, the maintenance of a high quality sand blasted finish on theextrudate contacting side of the cooling mandrel.

The best mode known to me to carry out this invention has been describedabove in terms sufticiently full, clear, concise and exact as to enableany person skilled in the art to make and use the same. It is to beunderstood, however, that it is within my contemplation that certainmodifications of the above-described mode of practicing the inventioncan be made by a skilled artisan without departing from the scope of theinvention and it is, therefore, desired to limit the invention only inaccordance with the appended claims.

I claim:

1. In apparatus for producing a web of expanded polystyrene comprisingan extruder for extruding a tubular extrudate, means for expanding theextrudate and a cooling mandrel over which the expanded extrudate isdrawn in surface to surface contact therewith, the improvementcomprising: a contacting ring for dressing the inside surface of theextrudate which is thin in the longitudinal direction relative to themandrel, which has an extrudate-contacting outside surface which ispositioned to contact the extrudate at a location where the extrudatehas reached its final diameter, which is disposed substantiallyconcentrically, with the mandrel and which is spaced longitudinallyupstream of the cooling mandrel. I

2. Apparatus according to claim 1 and further comprising a spacer ringwhich is thin in the longitudinal direction relative to the mandrel,which is disposed in the space between the contacting ring and themandrel and which is substantially out of contact with the extrudate tothermally isolate the contacting ring from the means used to cool thecooling mandrel.

3. Apparatus according to claim 2 and further comprising fastener meansextending through the spacer ring for attaching the contacting ring andthe spacer ring to the mandrel.

1. IN APPARATUS FOR PRODUCING A WEB OF EXPANDED POLYSTYRENE COMPRISINGAN EXTRUDER FOR EXTRUDING A TUBULAR EXTRUDATE, MENS FOR EXPANDING THEEXTRUDATE AND A COOLING MANDREL OVER WHICH THE EXPANDED EXTRUDATE ISDRAWN IN SURFACE TO SURFACE CONTACT THEREWITH, THE IMPROVEMENTCOMPRISING: A CONTACTING RING FOR DRESSING THE INSIDE SURFACE OF THEEXTRUDATE WHICH IS THIN IN THE LONGITUDINAL DIRECTION RELATIVE TO THEMANDREL, WHICH HAS AN EXTRUDATE-C0NTACTING OUTSIDE SURFACE WHICH ISPOSITIONED TO CONTACT THE EXTRUDATE AT A LOCATION WHERE THE EXTRUDATEHAS REACHED ITS FINAL DIAMETER, WHICH IS DISPOSED
 2. Apparatus accordingto claim 1 and further comprising a spacer ring which is thin in thelongitudinal direction relative to the mandrel, which is disposed in thespace between the contacting ring and the mandrel and which issubstantially out of contact with the extrudate to thermally isolate thecontacting ring from the means used to cool the cooling mandrel. 3.Apparatus according to claim 2 and further comprising fastener meansextending through the spacer ring for attaching the contacting ring andthe spacer ring to the mandrel.